Mike Hunter
Listen to my weekly FM radio show called Music With Space on 103.3FM in NJ or on the web at www.wprb.com each week at 1am EST to 4am EST

Are you using both the Benjolin AND the Zeitgeist??
Waaay cool. Love it!!

My son & I are troubleshooting the Zeitgeist. I played this track for him to show what it was supposed to sound like._________________The most important music equipment is what's in front of the instrument.

Increasing the feedback pot increses oscillations fed into the echo / delay circuit. I can make motorboat noises, spceship engine noises, and if I TWEAK JUST RIGHT...HIGH pitched bleeps and bloops... reverbed to all getout.

All this with ZERO input.

If I connect an input signal, it does not appear to affect the sound at all.

This thing has its own party going and won't let the neighbors in!

I did some rudimentary signal tracing and found that the output of IC2A (pin 1 on the quad opamp) is White noise.

Originally it seemed that the left switch on the zeitgeist (pre-post delay) could detune the keyboard sounds. And there were other ways of distorting/modifying the synth sounds. (modulation is the 2nd knob from left in my zeitgeist.) I can't explain its exact function because I'm a newby to electronics. I just labeled the knobs/switches the way Rob told me.

Now it mostly just shrieks & howls. Well, what did I expect, it IS an 'Alien transmission module'... just different aliens now! _________________The most important music equipment is what's in front of the instrument.

Increasing the feedback pot increses oscillations fed into the echo / delay circuit. I can make motorboat noises, spceship engine noises, and if I TWEAK JUST RIGHT...HIGH pitched bleeps and bloops... reverbed to all getout.

All this with ZERO input.

If I connect an input signal, it does not appear to affect the sound at all.

This thing has its own party going and won't let the neighbors in!

I did some rudimentary signal tracing and found that the output of IC2A (pin 1 on the quad opamp) is White noise.

Odd...the input signal should be "echoed." After all, the zeitgeist is based on an "echo" chip. There is a switch that enabled the light sensor and a switch that mixes the input signal with that of echoes. In the other position, the original signal is muted and only the echoes of it are left.

If no imput is connected and the feed back (the second knob from the left) is turn up high or completely, then the noise in the circuit is echoed and build up over time into that strange noise you hear.

If the turn the two knobs on the far right, you are altering the length of the echos from short on the left to long on the right.... as the echo time increases the sounds recorded "slow down" and thus, drop pitch. If turning from a long echo to a short the pitch increases in pitch.

If the two knobs are increased high enough, the echoes go beyond the parameters of the chip and cacophony ensues until it completely goes out and the sound disappears altogether.

Hope this description helps you understand how the unit sounds... I can create a youtube video showing this visually and with soundif this is useful to you. I can also do this for the benjolin for comparison sake.

Just let me know,_________________Mike Hunter

Listen to my weekly FM radio show called Music With Space on 103.3FM in NJ or on the web at www.wprb.com each week at 1am EST to 4am EST

My Benjolin seems to be working OK. It's the Zeitgeist that has a trip of it's own going right now. It's almost as if the "Clock" signal within the unit is too high a level and needs to be attenuated some. I was thinking of severing the link between pin 1 and 5 of the Quad Op amp and inserting a variable resistance in between to see if that would tame the thing a little.

The Zeitgeist has some design flaws, mostly to do with the CMOS reel-to-reel opamp that seems to have a will of their own. Replacing the CMOS opamp with a LM324 does help in cases, but there are some more things that need a little change in the design for a LM324. Basically the virtual ground for the opamps isn't always as stable as it should be and would be with the FET opamps like the TL074A I normally use. (The CMOS opamp was recommended by the Texas Instruments distributor as a problem-free reel-to-reel, low voltage, low power alternative for the TL074A. I fully relied on their advice, just as I had so little time to develop the Zeitgeist...)

In contrast to the Benjolin design, which has been a proved circuit over quite some years, I didn't have the time to really test the Zeitgeist design thoroughly. I built four Zeitgeists just prior to the workshops and all worked fine, so I thought all was ok. I am sorry that the Zeitgeist behaviour is a bit more mysterious as it was meant to be, and sometimes just gives up...

I am redesigning the Zeitgeist to make it as reliable as the other stuff I make. Until then no more Zeitgeist workshops...

The Zeitgeist has some design flaws
I am sorry that the Zeitgeist behaviour is a bit more mysterious as it was meant to be, and sometimes just gives up...
Until then no more Zeitgeist workshops...

/Rob

Hmmm, well that kinda sucks, what do I do with a non-functional Zeitgeist? Maybe take out the electronics and stick a bunch of LEDs in the box??

Oh yeah.... I don't need it anymore....I just got a Korg Electribe!!!!! It can make just as many weird sounds as the Zeitgeist... maybe I'll upload some samples tonite!_________________The most important music equipment is what's in front of the instrument.

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